1. Field of the Invention
This invention relates generally to a fluid pressure controlling device to be inserted in the fluid brake system of a vehicle having front and rear wheels.
2. Description of the Prior Art
In such fluid vehicle braking systems, if the driver actuates the brake pedal for applying a braking fluid pressure equally to all the vehicle wheels, the rear wheels are more likely to be subjected to locking, thereby giving rise to dangerous skidding.
The use of a so-called G-valve assembly in such braking systems for avoiding such dangerous skidding is well known. In these assemblies, a ball valve member rolls up an inclined ramp upon deceleration of the vehicle and seats on a valve seat when a predetermined deceleration is reached, whereby the rear brake wheel cylinders are isolated from the common master cylinder. It is also well known that when the vehicle load is large, the predetermined deceleration point is reached at greater fluid pressure of the master cylinder than when the vehicle load is small. However, with a G-valve assembly installed, even if further increased fluid pressure is applied after the valve closes, when the vehicle load is large, the increased fluid pressure is not supplied to the rear brake wheel cylinders, since, as already indicated, they are then isolated from the common master cylinder. Therefore, the fluid pressure applied to the rear wheel cylinder is under the ideal pressure level. The lack of such increased fluid pressure being applied to the rear wheel cylinders, however, puts too much brake load on the front wheel cylinders, i.e., it results in the lack of sufficient and proper braking force for the vehicle.
In addition, it is also well known that a so-called load sensing valve assembly, or a device combining the aforementioned G-valve assembly and a proportioning valve assembly, can be inserted into the braking system for obviating these drawbacks of the G-valve assembly. However, these load sensing valve assemblies have been too complicated in structure and too expensive to manufacture.